1. Field of the Invention
The present invention relates to a clutch apparatus for a vehicle for transmitting torque between a drive unit, such as an internal combustion engine, and a transmission. More particularly, the invention relates to a clutch apparatus capable of appropriately coping with time-course variations in characteristics of, for example, a clutch disk and an actuator.
2. Description of the Related Art
Generally, in a clutch apparatus for a vehicle, the attitude (posture) of a diaphragm spring varies with wear of clutch facing (a clutch disk), resulting in an increase in an operating force (a load imposed on a clutch cover) required to disengage a clutch (break the coupling). In order to cope with this problem, according to the apparatus disclosed in Japanese Patent Application Laid-Open (kokai) No. 215150/1993, the height of a fulcrum of a diaphragm spring is modified according to a load imposed on a clutch cover at the time of clutch operation (a load imposed on a sensor diaphragm fixedly attached to the clutch cover), so as to modify the attitude of the diaphragm spring, thereby compensating for variations in operating characteristics of a clutch associated with wear of the clutch facing.
In the clutch apparatus for a vehicle, there exists a sliding portion, located, for example, between the diaphragm bearing and a release bearing, between the release bearing and the input shaft of a transmission, or between a release fork and a fulcrum member on which the release fork pivots. The sliding resistance of the sliding portion varies according to the number of operations of the clutch apparatus (the number of changeovers of the state of the clutch disk from engagement with a flywheel to disengagement from the flywheel or vice versa). Also, the friction coefficient of the clutch disk is low at the early stage of use and then increases before it substantially plateaus at a predetermined magnitude. Furthermore, output characteristics of an actuator (for example, an electric motor) for moving the release fork through application of pressure vary with time. Accordingly, even when wear of clutch facing is sufficiently little not to raise a problem or even when the wear is compensated for by means of, for example, the above conventional technique, operating characteristics of a clutch (particularly clutch response characteristic) vary according to the number of clutch operations.
An object of the present invention is to provide a clutch apparatus capable of solving the above-mentioned problems in the conventional clutch apparatus.
To achieve the above object, the present invention provides a clutch apparatus for a vehicle, comprising a clutch disk disposed opposite a flywheel, which rotates unitarily with an output shaft of a drive unit; a pressure plate for applying a press-contact load to said clutch disk so as to press said clutch disk toward said flywheel to thereby engage said clutch disk with said flywheel; a diaphragm spring for causing said pressure plate to generate the press-contact load; a release mechanism for applying a force to a predetermined portion of said diaphragm spring to thereby deform said diaphragm spring for disengaging said clutch disk from said flywheel; and adjustment means for modifying the press-contact load according to the number of changeovers of the state of said clutch disk from disengagement to engagement or vice versa.
The adjustment means above mentioned modifies the press-contact load according to the number of changeovers of the state of the clutch disk from disengagement to engagement or vice versa, whereby clutch operation can be modified, for example, to compensate for variations in sliding resistance of the sliding portion. Therefore, the clutch can keep desired operating characteristics according to the present invention. Also, the press-contact load can be modified so as to be appropriate for a variation in the friction coefficient of the clutch disk according to the present invention.
Preferably, said adjustment means modifies the press-contact load such that the press-contact load decreases, continuously or stepwise, as the number of changeovers of the state of said clutch disk from disengagement to engagement or vice versa increases, in order to have an appropriate press-contact load for at least the friction coefficient of the clutch disk.
Alternatively, said adjustment means modifies the press-contact load such that the press-contact load decreases as the number of changeovers of the state of said clutch disk from disengagement to engagement or vice versa increases when the number of changeovers is smaller than a predetermined number, and the press-contact load increases as the number of changeovers increases when the number of changeovers is larger than the predetermined number, in order to have an appropriate press-contact load for at least the friction coefficient of the clutch disk.
Preferably, a clutch apparatus moves a member to apply the force to the diaphragm and said adjustment means modifies the press-contact load such that an actual stroke of said member under becomes equal to the estimated stroke of said member certain conditions to thereby make adjustment.
It is another object of the present invention to provide a clutch apparatus that can automatically compensate for time-course variations in clutch-operating characteristics without causing disadvantage to the normal driving of the vehicle by limiting the adjustment timing to a certain timing.
It is another object of the present invention to provide a clutch control apparatus that can automatically compensate for time-course variations in clutch-operating accurately by limiting the adjustment timing to a certain timing.
Other features and advantages of the present invention will be apparent from the following description taken in connection with the accompanying drawings.